The invention relates to a method for assigning a number of M data links located on the subscriber side, in particular ATM links, to a number of N data links located on the transport side such as, for instance, Ethernet links.
In particular in Ethernet networks, mainly in the WAN (WAN: Wide Area Network) domain, increasing use is being made of network elements that are interconnected by means of N parallel (bundled) Ethernet lines. Said Ethernet lines as a rule operate in each case in full-duplex mode and employ the same data rate. The necessary bundling of the N data streams in the receive direction and splitting into N data streams in the transmit direction is performed by the respective network element (a router or switch, for example).
This approach offers numerous advantages compared to a single link. It makes the overall link more failsafe, which impacts positively on its availability. Should-one of the N links fail, the data stream can be conveyed over the remaining N−1 links. There is also a cost advantage compared to a single link employing a high bit rate. It is often more favorable to install N links having a respective data rate D than to install a single link having the data rate N×D. Moreover, increased bandwidths can be implemented in existing networks because parallel networks or cabling arrangements are often already present that have hitherto been used only as single links. Being able to bundle data streams thus allows the existing infrastructure (cabling) to be retained but the data rate handled thereover to be increased. This solution further presents an additional option to the effect that a link's data rate can be matched in steps to the actual volume of data traffic by optionally adding further link lines. Thus the advantage can be gained thereby of not having to change up to the next generation of the networking standard (from 100Base−T to 1000Base−T, for example) if there is a bottleneck in the transmission capacity, but instead of being able to increase the data rate capacity in quite small steps in keeping with what is needed.
This approach to better utilizing the existing infrastructure is now also being applied increasingly in the area of what are termed Ethernet DSLAMs (DSLAM: Digital Subscriber Line Access Multiplexer). In traffic toward the backbone network (referred to below as upstream data traffic), DSLAMs of said type terminate incoming ATM data traffic and forward the Ethernet data frames contained therein to a router via one of the N Ethernet interfaces. In traffic toward the subscriber (referred to below as downstream data traffic), independently of the interface of their origin the arriving Ethernet frames are assigned on the basis of their target MAC address to the ATM link associated therewith, packed into AAL5 frames, and forwarded as ATM data traffic to the desired addressee (subscriber). The DSLAM thus performs a bridging function between the ATM layer and Ethernet layer (ATM to Ethernet bridge).
For the downstream data traffic there is thus a clear assignment of how to route the original Ethernet frames to the subscriber based on an assignment table (MAC addresses to ATM links). This task is thus the same for all Ethernet DSLAMs regardless of the number of available Ethernet interfaces on the transport side.
This matter is still unresolved for the upstream data traffic that has to be conveyed, for example, over the available Ethernet interfaces on the transport side to the backbone network. What can be problematic therein is that if an Ethernet interface fails owing to a fault or following an administratively initiated interface deactivation the ATM links on the subscriber side that were previously assigned to said Ethernet interface must in a suitable manner be re-linked on the transport side so as to avoid interrupting any data traffic possibly being handled. Conversely, it is of course also necessary for a deactivated Ethernet interface to be returned to operation as soon as possible after being successfully reactivated and to be incorporated into the data exchange process.